In both the military and commercial market places, there is an ever expanding use of radio-based geolocation/navigation devices (systems and methods described in this disclosure can be applied to both geolocation and navigation and are used interchangeably). Though they generally perform satisfactorily, in virtually every application there are instances where degraded accuracy or non-availability create dangerous situations. For military applications, degraded positional accuracy can affect the safety of troops or the navigation precision of a guided weapon. For commercial applications, the non-availability of GPS service inside a building can delay the arrival of emergency personnel to a 911 caller in distress.
Historically, much research has been done to improve the performance of GPS user equipment, yielding great gains in positional accuracy and availability. These activities have principally focused on improving the traditional functions in user equipment such as receiver sensitivity, reference oscillator stability, correlator speed, and signal processing algorithm performance. To create opportunities for large gains in performance, the present disclosure identifies new approaches and algorithms to apply to user equipment through aiding using augmentation sources including RF signals of opportunity (SoOPs). For the purposes of the present disclosure, a SoOP is a radio frequency (RF) transmission that is not intended for navigational position or timing purposes. Examples of SoOPs include cellular downlink broadcasts, WiFi access points, television signals, terrestrial radio AM and FM signals, etc. Therefore, the present disclosure represents a means to provide large gains in geolocation and navigation performance vs. diminishing incremental benefits from traditional GPS user equipment research topics. The goal is to be able to maintain the same level of accuracy as a GPS in GPS-unavailable environments, without adding significant system complexity, cost, or operational burdens. These gains can benefit the growing markets and applications in both the military and commercial sectors.
A robust navigation system using SoOPs is disclosed in commonly owned U.S. patent application Ser. No. 13/250,134 , titled “System and Method for Robust Navigation and Geolocation Using Measurements of Opportunity” (the “'134 Application”), and U.S. patent application Ser. No. 13/909,824, titled “Performance Improvements for Measurement of Opportunity Geolocation/Navigation Systems” (“'824 Application”), which are hereby incorporated by reference, follow this approach. The previously disclosed robust navigation system invented by the Applicant includes the use of SoOPs in a navigation solution, the application of cooperative simultaneous localization and mapping (C-SLAM) as a source measurement combining/estimation framework, the ability to synthetically time synchronize unsynchronized SoOPs, the ability to combine GPS measurements with other RF source measurements in a navigation estimation, the ability to extract and use time parameters from SoOPs, and the ability to discover and locate the position of a priori unknown SoOPs, the ability to use SLAM-derived navigation estimates in the GPS code and carrier tracking loops including extensions to other Global Navigation Satellite Systems (GNSS) sources, the ability to time tag RF signals at a node if the node local time source is not precise or available, the ability to include non-RF sources in the geolocation process, and the ability to dynamically change representation of landmarks to thus further enabling robust position, velocity and timing (“PVT”) estimates through conditions of GPS signal absence. The present disclosure uses these methods to proactively manage geolocation-related processing to lower processing requirements, enabling new embodiments.